High-pressure presses are often used for the densification of powdered or cast materials, such as e.g. turbine blades, to achieve elimination of material porosity. Thus, the pressing is applied to an article placed in the press in order to substantially increase the service life and the strength of the article, in particular the fatigue strength. Another field of application is the manufacture of products, which are required to be fully dense and to have pore-free surfaces, by means of compressing powder.
An article to be subjected to treatment by high-pressure pressing is positioned in a load compartment of a pressure chamber. After loading, the chamber is sealed off and a pressure medium, either a liquid or a gas, is introduced into the pressure chamber and the load compartment thereof. The pressure and temperature of the pressure medium is then increased, such that the article is subjected to an increased pressure and an increased temperature during a selected period of time. The heat is usually provided by means of a heating element or furnace arranged in a furnace chamber of the pressure chamber.
The pressures, temperatures, and treatment times are dependent on factors such as e.g. the material properties of the article to be treated, the field of application, the required quality of the treated article, and so on. The applied pressures and temperatures may typically range from 200 to 5000 bars and from 300 to 3000° C., respectively. When the pressing of the articles is finished, the articles often need to be cooled before being removed, or unloaded, from the pressure chamber.
A treatment of articles by high-pressure pressing is expensive, particularly the cost related to the residence time of the articles in the pressure chamber. Therefore, there has been a strive for providing a more efficient heating and cooling of the articles such to reduce the treatment times, still meeting the demands of the heating and cooling properties such as e.g. temperature gradients within specific limits.
To achieve an improved heating and cooling of the articles in the pressure chamber, it is preferred to circulate the pressure medium in the chamber. This circulation may be performed with our without mechanical aids. When used without mechanical aids, heat convection and re-distribution is provided due to existing or promoted temperature differences, as e.g. outer wall heating or cooling. Thus, the circulation is based on the observation that cooler fluid flows downwards and warmer fluid rises.
An example of such an heat convection high-pressure press is disclosed in patent document DE3833337. However, a problem related to this arrangement is that the heat circulation, related to the circulation of pressure medium, is difficult to control.
To overcome this problem, mechanical aids, such as a fan, may be used to improve the circulation of the pressure medium. In patent document U.S. Pat. No. 7,011,510, a pressure medium gas stirring fan is driven by a motor for promoting the temperature uniformity within the press chamber housing the articles.
Due to the high temperatures and the extreme pressures applied in a high-pressure press during operation, the equipment provided in the pressure chamber must meet high demands on durability, endurance, performance, and so on. This is especially the case for a motor provided in the pressure chamber, wherein the motor efficiency is susceptible for the high-pressure press conditions at operation. Thus, it is of important that a motor provided in a high-pressure press is arranged for the working conditions such that the service life of the motor is increased, thereby avoiding costly operation ruptures and/or troublesome maintenance.
However, a problem with the disclosed arrangement in the mentioned patent document is that the motor for driving the stirring fan is not suited for the high-pressure press working conditions. More specifically, the arrangement suffers from an unreliable motor operation, as the motor is liable to e.g. breakdowns and/or a low motor efficiency.